As I was unfamiliar with the expression, “think past something.” I looked for it in the headword of ‘think’ in Cambridge, Oxford online dictionary and OALD. None of them registers “think past something.”

I think I was confused with the insertion of ‘well’ between ‘think’ and ‘past,’ which can be interpreted both ways of ‘think well’ and ‘well past’

2 Answers
2

I don't think it is an idiom, but it is used routinely enough to be understandable. As you surmised, to think past something means to think beyond something, to jump to the next thing, instead of spending time on the "something" currently in front of you.

Also, to think past yourself means to think of things other than yourself. For example, in this Utah State Today article:

Noted humanitarian, award-winning and best-selling author,
documentary photographer and Navy SEAL Eric Greitens told Utah State
University graduates Saturday that they will be at their strongest in
life’s journeys when they are serving others. While speaking to Utah
State University’s graduating class of 2012, Greitens told the
students to think past themselves and to serve something larger.

As you figured out, in your example, the traveler was ready to dismiss Lisbon because she wanted to be gone from there and travel on to what she thought was the much-more-interesting destination of Oporto. So she wasn't giving Lisbon any thought at all, but was instead already anticipating Oporto. By looking ahead to what was coming next, she was missing out on what was right in front of her.

As you have surmised – and JLG confirmed – the expression alludes to thinking past one stop on an itinerary in anticipation of the next.

I've heard a similar expression used rather often in sports.

When a team will play against what is regarded to be a weaker opponent between now and when they are scheduled to square off against a more highly-touted rival, that first game is sometimes called a "trap game." If the team loses that game, fans and the media will wonder if they were looking past their first opponent (that is, were they so concerned about their second match, that they failed to adequately prepare for the first?).

The Cougars clearly should not be looking past the Bengals,
remembering all too well also last year’s game... →